1. Field of the Invention
The present invention relates to multilayer ceramic devices, and more particularly, to an improved structure related to external electrodes of a multilayer ceramic device, wherein the structure is made without both nickel plating and tin plating.
2. Description of Prior Art
Currently common multilayer chip passive devices include ceramic electronic devices such as multilayer ceramic capacitors (MLCCs), multilayer ceramic inductors (MLCIs), multilayer varistors (MLVs) and multilayer ceramic thermistors. Hereinafter, all these ceramic electronic devices are referred to as “multilayer ceramic devices”.
Referring to FIG. 1, an existing multilayer ceramic device 10 comprises a laminated ceramic body 20 having opposite end surfaces and comprised of a plurality of dielectric layers, a pair of external electrodes 30 each respectively attached to one end surface of the laminated ceramic body 20 and a plurality of alternately staggered internal electrodes 40 within the laminated ceramic body 20 configured in an alternating manner and electrically connected to the corresponding external electrodes 30 respectively.
Traditionally, the external electrodes 30 of the multilayer ceramic device 10 are electrically attached to contacts provided on a circuit board. Thus, the external electrodes 30 of the multilayer ceramic device 10 have to possess good resistance to soldering heat, corrosion and oxidation.
For this purpose mentioned above, in the process for manufacturing the multilayer ceramic device 10, nickel plating and tin plating are necessarily performed to make the external electrode 30 have the layered structure composed of an innermost conduction electrode 31 made of silver, an intermediate nickel plated layer 32 and an outermost tin plated layer 33, wherein the intermediate nickel plated layer 32 servers as an intermediate shield to protect the silver-made conduction electrode 31. Due to the poor resistance to soldering heat of nickel, the intermediate nickel plated layer 32 has to be covered with the outermost tin plated layer 33 so as to be adequately resistant to soldering heat.
However, the plating steps for making the multilayer ceramic device 10 can cause toxic waste seriously polluting the environment.
As shown in FIG. 2, with the development of SMT (Surface Mount Technology), the multilayer ceramic device 10 is now available as a surface mount device (SMD). With SMT that has been mature, the multilayer ceramic device 10 can be directly placed on the circuit board 90 with beforehand glue or tin paste 95 and fixed to contacts of the circuit board 90 by melting the paste 95 with hot air or infrared rays to its melting point and then cooling it, so as not to involve any soldering step as required by the traditional process.
That is to say, the external electrodes 30 of the multilayer ceramic device 10 are attached to the circuit board 90 by means of SMT, without using the traditional soldering steps. Therefore, it is no more needed to provide the external electrodes 30 of the multilayer ceramic device 10 with extra resistance to soldering heat and corrosion by building the nickel plated layer 32 and tin plated layer 33 thereon.